This invention is an improvement over the engine shut-down system disclosed in my U.S. Pat. No. 3,153,403 entitled "Engine Shut-Down System", which issued on Oct. 20, 1964. That device included a cylinder to which engine oil pressure was supplied, thereby forcing a piston within the cylinder to seat a ball valve so that engine fuel pressure supplied to the other end of the cylinder would normally not be supplied to a second cylinder and piston arrangement which would operate a shut-down device. However, should oil pressure drop below a predetermined level, the ball valve would open allowing fuel pressure to displace the piston in the second cylinder thereby closing an air intake to the engine and shutting it down. The pistons within both cylinders were provided with O-rings to minimize leakage of fluid past the pistons. However, it was found that in operation the pistons would vibrate considerably due to momentary changes in oil pressure. This would cause the O-rings to become heated due to friction and stick to the cylinder walls resulting in rapid deterioration of the O-rings at an unacceptably fast rate and also resulting in leakage of oil past the pistons into other parts of the cylinder. Thus, considerable maintenance expense was incurred due to this leakage.
Also, my prior art device included a spring which normally held the ball valve closed during initial rise in oil pressure so that the engine would not immediately shut down. However, should the fuel pressure, which builds up almost instantaneously, reach full pressure before the oil reached full pressure, the ball valve might be opened against the force of the spring causing the device to shut down the engine. This is a highly undesirable situation which causes much irritation to the engine operator in trying to keep the engine operating during build up of the oil pressure.